I'm new here, so this may be in the wrong place but here goes.
I downloaded winamp 5.093 on two computers. On one, Windows XP Home,
it plays both audio and vidio. On the other, Windows 98 SE, it only plays audio.
Is there some setting I am missing, or is this normal?
Thanks for any help.

I guess this is because of missing video codecs.
XP has a few built-in and most recent codecs support XP/Vista/2k

Win98 probably doesnt have any codecs apart from mpeg and some codecs don't work on Win98.
Divx 7 only works on XP and above, for example. You could look for alternative MPEG4 codecs but you're likely to run into weird problems.

Please could you tell me whether it is a virus or something wrong with
the Winamp music player which I am using.
My operating System is Windows 98 SE.
Music player: Winamp 5.094
After some time, maybe 25minutes maybe more Winamp goes soft, but the
music is playing - is there a virus that does this or is this version
of Winamp buggy?
Once I reboot the machine my WinAmp plays properly again. Could another reason be the number of open internet windows I have on my taskbar and that my memory resources are running out? Or could my memory (RAM) inside be faulty?